Fuel injection system for an internal combustion engine

ABSTRACT

A fuel injection system for internal combustion engines in which the control of the fuel injection valve member is controlled by controlling the pressure of a control chamber. The control chamber is either relieved by a 3/2-way control valve or made to communicate with a high-pressure fuel source. The control valve is designed such that the control valve has a valve body, which on both sides carries a valve sealing face, which cooperate with a first valve seat and second valve seat, respectively, and control the inflow of high pressure into or outflow thereof out of the control chamber. To vary the dynamics of the control events, the valve body, upstream of the second valve sealing face, has a throttle gap, and downstream of the first valve sealing face the valve body has a collar, between the collar and the throttle gap a pressure conduit leads away to the control valve, the inflow and outflow to and from which is thus varied.

PRIOR ART

The invention is based on a fuel injection system for internalcombustion engine. In one such fuel injection system, known from GermanPatent Application DE-A 44 06 901, the electromagnetically driven3/2-way control valve that electromagnetically controls the pressure inthe control chamber is designed such that in one position, the controlvalve connects the valve chamber with the high-pressure fuel source,which then also communicates with the control chamber at the same time,and in another position connects the valve chamber and at the same timethe control chamber with the relief chamber. A throttle is formeddownstream of the valve seat in the control valve in the outflow conduitthrough which the relief speed and consequently the opening rate of thefuel injection valve member can be reduced at the injection onset. Onthe inlet side to the control chamber, conversely, no flow limitation isprovided, so that the end of the fuel injection event can be effectedrapidly by means of a rapid pressure buildup in the control chamber thatputs the fuel injection valve member into the closing position. Thisarrangement has the disadvantage that the outflowing fuel, by thediversion process of which the fuel injection onset is intended to beinitiated, is throttled downstream of the valve seat, which leads to apressure buildup upstream of the throttle. If the diversion occurssuddenly, the result is feedback forces on the control valve member,which adversely affect the switching times of the control valve becausethey counteract the controlling motion of the valve member. The finaloutcome is that injection quantities in successive injection events varyconsiderably.

ADVANTAGES OF THE INVENTION

With the fuel injection system according to the invention hydraulicsurges that occur as pressure fluid and is diverted from the controlchamber to the control valve member have hardly any effect on theuniformity of the injection events. Disruptive feedback is averted bythe throttle located upstream of the valve seat. It is advantageous thatthe throttle is realized on the valve body without requiring anyadditional component or additional machining steps. In an advantageousrefinement, an additional damping of the hydraulic surges on the valvebody is effected. The collar has the effect that the quantity ofpressure fluid flowing into the valve chamber, which quantity is meantto be delivered for control purposes to the control chamber, isthrottled downstream of the valve seat and by a pressure buildup, anadditional force on the valve body in the opening direction thereof iscreated. Thus, the pressure required to terminate the injection can bebuilt up more rapidly in the control chamber. The result is accordinglyfaster switching times of the control valve. When the second valve seatopens, in the process of which the valve body moves in the closingdirection to the first valve seat, a delay upon closure of the valveseat occurs because of the presence of the collar, and thus a delay inthe relief of the control chamber and a corresponding desired delay,already sought by the throttle, in the pressure rise at the injectionvalve member.

Further advantages of the invention can be learned from the ensuingdescription in conjunction with the drawing.

The FIGURE illustrates a fuel system in combination with a crosssectional view of a control valve.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

FIG. 1 is a simplified illustration of a fuel injection valve 1, whichhas an injection valve housing 2 with a bore 3 in which an injectionvalve member 5 is guided. On one end, the injection valve member has aconical sealing face 6, which cooperates with a conical valve seat 7 onthe end of the bore. Downstream of the valve seat 7, there is at leastone fuel injection opening 8, which when the sealing face 6 is mountedon the valve seat 7 is disconnected from a pressure chamber 10. Thepressure chamber 10 can be made to communicate via a pressure line 12with a high-pressure fuel source in the form of a high-pressure fuelreservoir 14, which is supplied with fuel, brought to injectionpressure, from a tank 11, for instance by a high-pressure pump 4 thatfeeds at a variable feed rate. The pressure in the high-pressure fuelreservoir can, however, also be controlled by means of a pressurecontrol valve 9 as a function of the signal of a pressure sensor 13, bythe diversion of a fuel quantity required for maintaining the pressure.In the region of the pressure chamber 10, the injection valve member hasa pressure shoulder 16, pointing toward the valve seat 7, upon whichshoulder the high fuel injection pressure prevailing in the pressurechamber 10 acts on the injection valve member 5 in the openingdirection. On the side of the injection valve member remote from thepressure shoulder 16, the injection valve member continues in the formof a connecting part 19 extending as far as a spool-shaped end 20 of theinjection valve member. In the region of the connecting part, theinjection valve member has a spring plate 22, between the spring plateand the housing 1 of the fuel injection valve, a compression spring 21is fastened that urges the fuel injection valve member into the closingposition.

The spool-like end 20, with a face end 24 that forms a movable wall andhas an area larger than that of the pressure shoulder 16, defines acontrol chamber 25 in the housing 2 of the fuel injection valve, fromthe control chamber a pressure conduit 26 leads away into a valvechamber 27 of a control valve 28.

The control valve 28 is embodied as a 3/2-way valve and has a controlvalve member 30, with a valve tappet 31 that is guided in a tappet guidebore 32 in the housing 33 of the control valve 28 and protrudes with oneend into the valve chamber 27. There, the tappet has a valve body 35,which on its side toward the tappet guide bore 32 has a first valvesealing face 37. The first valve sealing face cooperates with a firstvalve seat 38 that is formed at the transition from the tappet guidebore to the valve chamber 27. Opposite the entrance of the tappet guidebore 32 into the valve chamber 27, an outflow conduit 39 communicatingwith a relief chamber leads away from the valve chamber 27; an exit fromthe valve chamber 27 is embodied as a second valve seat 41 of thecontrol valve, with the seat a second valve sealing face 42 of the valvebody 35 cooperates. The control valve member is actuated by an actuatorwhich is controlled by a control device 36 and is not shown here, suchas an electromagnet or a piezoelectric drive means, which can also bedesigned in step-up fashion, and in the process moves with its valvebody back and forth between the first and the second valve seat. Thecontrol device controls the pressure in the high-pressure fuel reservoir14 with the aid of a pressure detector, such as the pressure sensor 13.The tappet guide bore 32 acts as an inflow conduit, in that the valvetappet 31, adjacent to the first valve sealing face 37, and togetherwith the wall of the tappet guide bore 32 forms a recess 45 in the formof an annular chamber, into which an inflow conduit 44 discharges thatcommunicates continuously with the high-pressure fuel reservoir.

In the region between the two valve seats 38, 41, the pressure conduit26 leads away from the valve chamber 27 to the control chamber 25.

The second valve sealing face 42 is provided on the face end of acylindrical spool part 46, which has a cylindrical jacket face thattogether with a cylindrical wall of the valve chamber forms an annularthrottle gap 47, by which a throttle is thus formed upstream of thesecond valve seat 41; this throttle controls the rate of fuel outflowfrom the control chamber 25 via the valve chamber 27 to the outflowconduit 39 or the relief chamber. If the control valve member is openedby the electromagnet, then the fuel can then escape only in throttledfashion. Since the throttling takes place downstream of the valve seat,however, pressure surges have little effect on the motion of the valvebody 35, since in contrast to the situation on its end toward theoutflow conduit, the valve body is force-balanced inside the valvechamber 27.

The valve body 35 also has a cylindrical collar 49, spaced apart fromthe first valve sealing face 37 toward the valve chamber 27. The collartogether with the wall of the valve chamber adjoining the circumferenceof the collar forms an annular gap 50, which between itself and thecylindrical spool part 46 forms an annular chamber 51. The pressure line26 branches off from the annular chamber to connect the valve chamber 27to the control chamber 25. When the first valve sealing face 37 is incontact with the first valve seat 38, a valve pressure chamber 52 isenclosed between the collar 49 and the first valve seat 38. The pressureof this pressure chamber acts on a shoulder 53 of the collar 49 in sucha way that as soon as the first valve sealing face 37 lifts away fromthe first valve seat 38, high-pressure fuel from the inflow conduit 44flows into the valve chamber 27 and a force component acts on the collar49 and thus on the control valve member 30, and the force componentseeks to reinforce the above-described opening motion. The pressurebuildup in the control chamber 25 and at the same time the terminationof the injection event by the injection valve thus proceed faster. Inthis event, the second valve sealing face 42 is at the same time broughtinto contact with the second valve seat 41, and the outflow conduit 39is closed.

In the opposite case, that is, if the pressure in the control chamber 25is to be decreased, in order to trip the injection, the valve body 35moves in the opposite direction from what is described above. The fuelflows in throttled fashion out through the throttle 47 at the secondvalve seat 41, and the switching motion of the valve body counteractsthe pressure in the valve pressure chamber 52, which leads to a delay inthe switching motion of the control valve member 30. This is desirable,because for the sake of noise and emissions, the onset of injectionshould occur slowly. Since in this exertion of force on the valve body35 the pressure in the annular chamber 51 between the collar 49 and thecylindrical spool part 46 is also operative, the gap width of theannular gap 50 of the collar 49 from the wall of the valve chamber 27and the width of the throttle gap on the cylindrical spool part must beadapted to one another. The valve seats 38, 41 and the valve sealingfaces 37, 42 are advantageously embodied conically. The tappet guidebore 32 and the outflow conduit 39 continue to be located coaxially toone another as shown in the drawing.

The cylindrical spool part 46 is adjoined, via a connecting part 55 ofreduced diameter, by a compensation spool 54, which dips into theoutflow conduit 39 and toward the wall thereof forms a gap ofsubstantially greater width than the width formed at the throttle gap47.

Because the tappet guide bore 32, on its end that has the first valveseat 38 or as a result of the end face that forms when the first valvesealing face 37 is seated on the first valve seat 38, is larger towardthe valve chamber 27 inside the recess 45 than the boundary area towardthe tappet of the recess 45, the control valve member 30 can be slightlyprestressed in the direction of the valve chamber 27 by the pressure inthe inflow conduit 44. This force acting in the direction of opening thevalve formed by the first valve seat 38 and the first valve sealing face37 cooperates with a compression spring, not shown here, of the actuatorand at the same time acts in the direction of closure of the valve atthe outflow conduit 39 formed by the second valve seat 41 and the secondvalve sealing face 42. This is especially favorable in the case of anelectromagnetic actuator, which is without current in this switchingposition.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. A fuel injection system for internal combustion engines,comprising a high-pressure fuel source (14), a fuel-injection valve (1)is supplied with fuel from said fuel source (14), said fuels injectionvalve includes an injection valve member (5) which is opened under apressure of a fuel delivered from said fuel source, the fuelcommunicates at least indirectly with a movable wall (24) that defines acontrol chamber (25) which receives fuel from a pressure conduit (26),the pressure conduit (26) communicates continuously with a valve chamber(27) of a control valve (28), the control valve (28) includes a controlvalve member (30) which communicates with an inflow conduit (44) andcontrols fuel flow to the valve chamber (27) coming from thehigh-pressure source, the valve chamber (27) communicates with anoutflow conduit (39) that leads to a relief chamber, a valve tappet (31)controls the control valve member (30) and the control valve member (30)has a valve body (35) that protrudes into the valve chamber (27), thevalve control member (30) is provided on a first side with a first valvesealing face (37) and on a second side with a second valve sealing face(42), each valve sealing face pointing in one of the directions ofactuation of the valve tappet, so that, depending on the position of thevalve body, the first valve sealing face (37) can come into contact witha first valve seat (38), whereupon the communication of the inflowconduit (44) with the valve chamber (27) is closed, and alternativelythe second valve sealing face (42) can come into contact with the secondvalve seat (41), whereupon the communication between the valve chamber(27) and the outflow conduit (39.) is closed, a throttle (47) isprovided in a communication between the valve chamber (27) and theoutflow conduit (39), the first valve seat (38) being formed at theorifice of a tappet guide bore (32) that guides the valve tappet (31) inthe valve chamber (27), and a portion of the valve tappet (31) locatedupstream of the first valve sealing face (37) has a recess (45) thatcommunicates continuously with the inflow conduit (44), the valve body(35) has a cylindrical spool part (46) which is spaced apart from thefirst valve sealing face (37) toward the valve chamber (27), and on aside remote from the first valve sealing face (37) carries the secondvalve sealing face (42) of the valve body (35), and the cylindricalspool part (46) together with the cylindrical wall of the valve chamber(27) has a throttle gap that forms the throttle (47), wherein the valvebody (35) has a cylindrical collar (49) which is spaced apart from thefirst valve sealing face (37) toward the valve chamber (27) and togetherwith the cylindrical wall of the valve chamber (27) forms an annular gap(50), wherein between the collar (49) and the cylindrical spool part(46) an annular chamber (51) is formed, from which the pressure conduit(26) branches to connect to the control chamber (25).
 2. The fuelinjection system of claim 1, in which the outflow conduit (39) leadsout, coaxially to the axis of the cylindrical spool part (46), from thesecond valve seat (41), and in the outflow conduit (39), a compensationspool (54) adjoining the cylindrical spool part (46) is adjustabletogether with the control valve member.